The US National Transportation Safety Board (NTSB) issued an investigation report on an accident occurred on July 2015, during off loading operations of a bulk carrier, in the Port of Galveston, Texas, that led to injury of two longshoremen.
The incident
On July 8, 2015, at 0857 local time, the Singapore-flagged bulk carrier Asia Zircon II was discharging a cargo of wind turbine towers in the Port of Galveston, Texas, when the lifting wire rope for one of the ship’s two cranes parted while hoisting a tower section out of the cargo hold. The wire failure caused the tower to fall back into the hold, damaging the tower and other tower sections in the hold. Two of the five longshoremen inside the cargo hold at the time suffered non-life threatening injuries. There was no reported pollution. Damages were estimated to exceed $1.5 million.
Probable Cause
The National Transportation Safety Board determines that the probable cause of the failure of the lifting wire rope of crane no. 4 on the bulk carrier Asia Zircon II was inadequate lubrication due to ineffective maintenance resulting in excessive wear of the wire rope.
Conclusions
- The incident was precipitated by a failure of the wire rope used in the lifting mechanism of crane no. 4. When the wire rope failed, the sling on the end of the tower base gave way, causing a failure in the strap on the other end so that the tower base fell back into the hold.
- The wire rope that failed showed signs of inadequate lubrication—that is, the lubricant applied was not distributed down into the inner wire surfaces. This resulted in excessive wear on the wire contact surfaces, particularly those not near the surface where the lubricant was applied. The areas of excessive wear become centers of nucleation for cracks that propagated in the individual wire strands creating stress concentrations that lead to wire failures gradually reducing load capacity of the rope, until it failed on July 8, 2015.
- Examination of the free end of the failure (the end that was not pulled through the lifting block) verified that the interior surfaces of the wire-to-wire contact showed many signs of inner strand wear (exhibited by typical inner strand wear notches— flattened areas on the wire that become centers of failure initiation), and these locations were the places where the failure occurred.
- Further evidence of inadequate attention to maintenance of the wire rope was found in the condition of the wire rope surface in the working portion of the cable provided that had not been pulled through the lifting block components. The wire showed evidence of multiple broken surface strands at the maximum stress locations consistent with normal wear and tear that should have been observed as a part of a proper routine maintenance process. The surface failures are persuasive in the preserved wire rope and are evidence that the wire rope was near or beyond its recommended useful life.
Recommendations
The NTSB advises the following, on maintenance of lifting gear and on crane operations:
- Inspection, maintenance, and management of wire ropes are essential to the prevention of accidents.
- A deteriorated wire rope directly affects the ability to safely and reliably handle loads up to the rated capacity of the crane.
- Crane operators, signalmen, riggers, safety observers, and crewmembers should adhere to manufacturer operating guidelines, design limitations, safety precautions, and inspection and maintenance procedures.
- Workers participating in crane operations should ensure that they remain in a safe area during a hoist. Entering the drop zone while the hoist is in progress puts them at risk.
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Source: NTSB
